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RFC1179 describes a set of fields that MAY appear in the control file. It is silent if other ones can appear as well. Unfortunately, some implementations will reject jobs unless they contain ONLY fields from a very small set. In addition, RFC1179 is silent about the ORDER the fields can appear.
LPRng quite happily will accept jobs from poor or nonconforming RFC1179 spooler programs, and fix them up to be conformant.
If you are sending jobs to one of a non-conforming spooler, you can force LPRng to send jobs with only the fields described in RFC1179 by setting the the :bk: (BacKwards compatible) flag in the printcap for your printer.